Telephone system



24 1927. May F. T. MADSEN TELEPHONE SYSTEM Filed March 28. 1924 InusnZUr- Fred T. Had sen Patented May 24, 1927.

UNITED STAT ES PATENT OFFICE.

FRED T. MADSEN, OF MAYWOOD, ILLINOIS,.ASSIGNOR, BY MESNE ASSIGNMENTS, TO AUTOMATIC ELECTRIC INC., OF CHICAGO, ILLINOIS, A CORPORATION OF DELA- \VARE.

TELEPHONE SYSTEM.

Application filed March 28, 1924. Serial No. 702,506.

The present invention relates to telephone systems in general, but is concerned more particularly with telephone s stems employing noi'i-numerical primary and secondary trunking systems.

The main object of the invention is the production of a new and improved.non'numerical trunking system in which a plu rality of backward hunting finder switches and a plurality of forward hunting secondary switches linked together in pairs through an intermediate distributing frame, are providec Another object is the production of new and improved circuit arrangements whereby a finder switch is prevented from starting in search of a calling line, and another finder switch is started instead, if all the outlets to first selectors associated with the first mentioned finder are in use.

Still another object has to do with the provision of the necessary circuit arrangements whereby the finder allotter, common to a plurality of finders, contains all the necessary starting and testing relays forthe finders and for the associatedsecondary switches, only one connectingrelay being provided for each finder and its associated secondary switch. As regards this feature, the present case may be considered an improvement on the co-pending application of Stehlik, tiled December 23, 1922, Serial No. 608,76 i.

The other objects have to do mainly with the circuit details and are more or less incidental to those pointed out above, and. to-' gether with the foregoing, will be explained fully in the course of the description which to follow. Y

Referring now to the drawings comprising a single sheet, the line of substation A terminates at the exchange in the banks of the finders, such as F. and also in the banks of the connector switches (not shown). The secondary switch SS associated with the finder F through the jumpers on the intermediate distributing frame IDF, extends the calling line found by the finder F to a selector, such as S.

The subscribers lines are divided into groups, and there may be as many lines in a group as there are sets contacts in the bank of the finder F, there being a sufiicient. number of finders provided for each group of lines to handle the trafiicfroin that group.

Also the first selectors, such as S,'are divided into groups, and there may be as many selectors in one group as there are sets of contacts in the bank of the secondary switch SS. The number of groups of lines, which is also the number of groups of finders, is of course determined by dividingthe total number of lines by the number of lines in a group. The number of groups of first selectors is determined from a consideration of the total number of selectors which are required to handle the traffic carried by all the groups of finders, as given by the standard tratlic curves. This figure, that is, the figure denoting the total number of selectors, is divided by the number of selectors in a group and the result gives the number of groups required. The secondary switches paired with the finder switches are then assigned to the selector groups so that here will be about the same number having access to the selectors in each group. Now in order that the entire system may be woven into one unitary network, the finders in the same group are, as far as possible, cross connected on the intermediate distributing frame to secondary switches in different groups. For example, if there are six finders, such as F, in one group, each finder is cross-connected with a secondary switch in a different group provided there are six secondary groups. However, if there are only three groups of secondary switches and six finders in one group, two finders are crossconnected with two secondary switches in each of the three secondary groups.

From the above, it will be appreciated that the conductors associated with the finders may be permanently wired to the one side of the intermediate distributing frame and that the conductors associated with the secondary switches may be. permanently wired to the opposite side of the distributing frame, permitting jumpers to be run from the finder side to the secondary side to cross-connect the finders and secondaries in any desired manner when the original installation is made, and also to permit the finders and secondaries to be readily regrouped. at the distributing frame from time to time as traffic conditions make it necessary or desirable. I i I The finder allotte r FA. contains the necessary start relays and testing relays for the finder .F and the secondary switch SS and also allots a new finder for use when the previously allotted one connects with a calling line.

The busyingrelay 58 is energized by the chain of relays, of which relay 5% one, when all the such as 5, associated with the secondary switch SS become busy. Relay 58 renders all the finder switches which are connected to the secondary switches in that group noirselectable to the finder allotter as. so that the tinder allotter FA will allot finders connected with secondary switches in idle groups only.

The substation A is an automatic substation having the usual talking, signalling, an switch controlling devices.

The finder F is mechanically of the well known rotary type 01. switch whose wipers have no normal position and move in a forward direction only. The secondary switch SS is identical niechanic:-illy with the finder F. The finder allotter FA is also identical with the finder F. except that it has six wipers instead of three. Although it is notessential to the :t'eatures of the invention, it is assumed that the selector S, whose circuits are only partially disclosed, is of the usual vertical and rotary type, having its bank contacts arranged in horizontal rows or levels.

The apparatus, havingbeen described more or less in general, will now be described in connection with the detailed description of its operation. For this purpose it will be assumed that the subscriber at substation A desires to make a call, in which. case he removes his receiver, closing a bridge across the line conductors 2 and 3. then this occurs, line relay 6 energizes through arniatures 7 and 10 of cut-oil relay 5 and places ground on start conductor 14 at arn'iature 1.3. Line relay 6 also disconnects the private normal conductor l from cut-oil relay 5 and connects it to ground at armature 11, thereby making the calling line busy immediately in the banks of the connector switches having; access to it. Relay 6 also connects the test conductor l, extending to the bank of the finder F, to cut oft relay 5, thereby placing a battery potential upon the said test conductor at to enable the finder F to be stopped on the calling line.

Responsive to the ground potential being placed on start conductor 14. start relay 68 ot the finder all tter FA energizes through the resting contact and armature 78 of relay (39; connects the lower winding of test re lay 67 with test wiper 22 ot the finder F at armature 75, through test wiper 84, the bank contact upon which it is standing, conductor .90, and the resting contact and armature 27; ans closes at armature 74 a circuit for stepping magnet 2a of the finder F, which includes armature 72 and its resting contact, wiper 81, the bank contact upon which it is standing, conductor 87, the resting contact and armature 4:0, and the self-interrupting contacts of the stepping magnet 24. The further operation depends upon whether the wipers 21-23, inclusive, of the finder F are standing upon the bank contacts of the calling line or upon some other set. Asstoning first that they are stz'indi'ng upon the bank contacts of the calling line, the lower winding of test relay 6?, which, as above pointed out, is connected with the test wiper 22 of the finder F, is energized over conductor 4; and througl'i cut-oil relay 5 and opens the circuit of stepping magnet 24 of the finder F at armature 72 before the said stepping magnet 2% has had time to energize. The finder is thus prevented from rotating and the wipers remain in engage ment with the contacts or the calling line. In the present case, however, it will be assumed that the wipers ot' the finder F are standing upon a set of contacts other than those of the calling line. In this case, no

circuit is closed ii'nniediately over test wiper 22 for test relay 67 and the wipers 2123, inclusive, of the finder F are advanced. step by step in search of the calling line due to Fill the buzzer-like action of stepping magnet 2a which interrupts its own circuit.

lVhen the wipers 2123, inclusive, of the finder F arrive upon the bank contacts in which the line of substation A terminates, test relay 67 is energized .in series with cutoff relay 5 ol the calling line over the above traced circuit. Cut-oil relay 5, how ver, beingmarginally adjusted, does not encrgize at this time, owing to the fact that the resistance of the lower winding ot relay 6'? limits the current flow through the said cutotl" relay Relay 6?, upon energizing, disconnects stepping magnet and prepares a circuit for relay 2-5 of the finder F at armature 72, and at armature 3 closes a locking circuit for its upper winding through armature (it) and its workin tact of start relay 68 The turther operation depends upon whether or not the secondary switch ffitil has already it an idle trunk.

Returnlng now to the points at which start relay 68 first energized, this relay, in addition to ClOSlDQ the above pointed out circuits for controlling the finder F, starts the secondary switch SS as tollows: At.

armature 2'6 relay circuit for test relay (i6 and stepping i, 35 ot the secondary switch SS in series. this circuit includes wiper as, the bank contact upon which it is standing, conductor 9:3, armature 39 and its resting contact. and the jumper 31. Coincident with the closure of the above circuit, test wiper 3T connected to the above circuit at a point betwcentest relay 66 and stepping magnet 35 at armawhich it is standing, conductor trunk and stepping magnet contact. working contact and arn'iatureturc 77, armature 77 being connected to relay 66 through armature 64: and its resting contact; and the working contact oft. armature 77 being connected to test wiper 37 through wiper 85, the bank contact upon 91. and the jumper 32.

From this point the operation depends upon whether the trunk upon which the wipers of the secondary switch SS are standing is busy or idle. It it is idle, the connecting up of test wiper 3? does not have any particular utility at this time and test relay 66 energizes immediately in series with stepping magnet Assuming the trunk to be busy, however, test relay 66 is short circuited by the ground potential encountered upon the grounded release trunk conductor of the busy trunk by test wiper 37 and does not energize. and stepping magnet 35 is energized through test wiper 3'? andinterrupts its own circuit. thereby advancing the wipers 3638, inclusive, step by step in search of an idle trunk.

Vhen an idle trunk is reached. which trunk it will be assumed the one con'iprising conductors 53 55, inclusive. and extending to the selector S, there is no ground potential present on the test conductor ot such ceases to operate. Also test relay 66, being no longer short circuited, energizes in series with stepping magnet 35. St'e 'rping magnet 35, however, does not energize in series with test relay 66, owing to ance of the latter. Upon energizing. test rclay 66 closes a locking circuit for its upper winding at armature 62; disconnects stepping magnet 76 from the auxiliary test wiper 83 and shunts the interrupter contacts of stepping magnet at armature disconnects test wiper 37 of the secondary switch SS from the junction (it its own winding and that of stepping magnet 35 and connects it to ground at armature 64, thereby making the seized trunk busy immediately: and at arn'iature 71 .prcpares a circuit for connecting relay 25 of the finder F.

Responsive to the energization of relay 66 or to the cnergization of relay 67. whichever is completed last. the circuit of connecting relay 25 is completed and is as follows: from ground by way of the working contact and armature Tel. armature T2 and its working 71, wiper 82, the bank upon which it is standing, conductor 88. and connecting relay battery. Upon energizing. relay locks itself to the release trunk conductor of the selector S. atarinature 28, which is at this time grounded through wiper ot the finder allo'ter FA: disconnects cut-oft relay 5 of the calling line from the lower winding of test relay 6'? of the finder allotter FA at arthe relatively high resist-' not vdeenergize tor the time mature 27 andconnects it to ground instead;

' line. Line relay 6 now deenergizes and removes ground from the start conductor 14 at arn'iature 13', opens the initial circuit of cutotl' relay 5 at armature 12, leaving cut-0t? relay 5 energized through its locking circuit which includes armature 8 and its working contact: and at armature 11 disconnects ground locally from the private normal conductor .i: and connects the said private normal conductor 4 to the cut-oft relay 5, whereby the private normal conductor 4: is maintained grounded as long as ground is supplied to energize the cut-off relay 5. Y

In the selector S, line relay t1 energizes over the calling line, responsive to the attraction ot armaturcs 26 and 29 of the connecting relay 25, and closes at armature 44 a circuit for release relay 42. Release relay l2 thereuponenergizes and places ground upon the release trunk conductor 54 at armature 45 so as to maintain'the connecting relay 25 energized after its initial circuit has been broken by the finder allotter FA.

In the finder allotter FA, as a further result of the application of the ground potential to wiper 82 to operate the connecting relay 25, as above pointed out, a circuit is closed for relay 69 which thereupon energizes; disconnects 76 at armature SO; and at armature 79 connects the stepping magnet 70 in multiple with itself. Stepping magnet 70 thereupon energizes and moves the associated pawl (not shown) into engagement with the next notch in the wiper driving ratchet wheel but does not move the wipers 8186, inclusive, the construction of the switch being such that the wipers are advanced upon the back stroke rather than upon the front stroke of the stepping magnet 70. Stepping magnet 70 also opens its local interrupter contacts but it does not interrupt its own circuit at this time, owing to the fact that the said interrupter contacts are bridged by arn'iature 63 and its working contact of test relay 66. As a further result of the energization of relay 69, it disconnects start relay 68 from the start conductor 14- at armature 78. Start relay 68. however. beingslow acting. does being and holds its armature proper attracted long enough to permit the release relay 42 'ot the selector S to become energized and ground the release trunk conductor 54: as above pointed out.

at another point the auX- iliary test wiper 83 from stopping magnet iii During this interval, cut-ofi relay energizes and line relay 6 deenergizes as hereinbefore pointed out, thereby removing ground from start con-d1 3t 14,- at armature 13.

the slow ac and opens the in relays 69 and ot .3 l magnet O at armature 74. This circuit, however, is now maintained closed by the connecting relay of the finder F which is locked up through jumper 32 and wiper 3. to the grounded release trunk conductor oi the selector Relay 68 also opens the locking circuits of test relays (3G and (31' at arn ature 73, whereupon these test relays decnergize. Test relay 66 ren'ioves the shunt "from aroiuid the sellinterrupting contacts ot the stepping magnet 70 at armature whereupon stepping magnet 70 deenergizcs and advances th wipers 81456, inclusive, into e -uiuut with the ne:-;' set of bank contiu It the tinder associated with the next ot con sets is busy, test wiper 82 engages grcuuideu bank contact and relay (39 remains ener ized, extending the ground potential to stepping magnet 'Zt), whereupon the sad stepping 'niagnet 7O continues to operate until an idle finder is reached, whereupon test wiper 82 engages an ungrounded haul: contact and relay 69 deenergizes again connecting start relay 68 to the start conductor l t to permit the pre-selected tinder to be started as soon as start conductor 1% again becomes grounded'upon the next call being made.

When the calling subscriber manipulates his calling device in accordance with the first digit in the desired number, line relay 41 of the selector S responds and the selector S raises its wipers -52, inclusive, in the usual manner opposite the desired level of bank contacts and then selects an idle trunk, whereupon switching relay -13 energizes; disconnects ground from armature let ot' the line relay 4L1 at armature l9; disconnects the test wiper 51 from the test circuit and connects it to the grounded release trunk conductor 5d at armature L7, thereby making the seized trunk busy immediately; and at armalures d6 and 48 disconnects the trunk conductors 53 and 55 from the windings of line relay t1 and extends them by way of wipers 50 and 52 to the line relay oi the switch associated with the seized trunk. The line and release relays (not shown) of the seized trunk now ener ize and the latter places ground upon the associated release trunk conductor, extending ground through test wiper 51 and armature QT and its working contact to the grounded release trunk conductor 54;, before the slow acting release relay 42 has had time to deenergize. The remaining part of the connection is estab lished in the usual and well known manner.

Vi hen the conversation is completed, ground is removed from test wiper 51 of the selector S in known manner upon the re ceiver being replaced at substation A, where upon the tinder F tests idle to the finder allotter Fri, and relay l3 otthe selector S and connecting relay 25 of the finder F de energize, Relay 25 opens the circuit of cutott' relay 5, whereupon cut-oil relay 5 decnergizes also.

The arrangement for causing idle finders to test busy to the finder allotter FA when the associated secondary switches have no idle outlets will now be explained. The group bus ring relay 58 has its circuit closed when all the chain relays, such as 56, are

energized. Each of these relays is connected to the release trunk conductor of a selector switch in the same manner as relay 56. Accordingly, when all the selector switches accessible to the secondary switch SS are busy, all the rcl: s, such as 56, are energized and the circuit of the group busying relay 58 is completed. Upon energizing, relay 58 grounds all the auxiliary test conductors, such 59, in the associated group. Considering the test conductor 59, when this conductor is grounded, ground is extended through the intermediate distributing frame jump-er ill to the auxiliary test conductor 89 of the finder allotter FA and, assuming that the tinder F is the one that is pro-selected when conductor 89 becomes grounded, a circuit is closed through the auxiliary test wiper 83, armature 80 and its resting contact, and the resting contact and armature (58 for the self-interrupting stepping magnet 70. Accordingly, stepping magnet 70 is ad vanced to the next set of cont-acts. If this next set of contacts tests busy to either of the test wipers S2 and 83, the wipers are advanced still further and they continue to be advanced until both wipers engage ungrounded contacts, it being understood, of

course, that the various finders in the same group with F are cross-connected to different secondary groups, so that when all trunks in one secondary group are busy, others may be still available in other secondary groups.

It may happen that the auxiliary test conductor 89 becomes grounded while the tinder F and the secondary switch SS arc operat ing due to the fact that the start relay 68 is energized responsive to a call. In this case, the wipers 8186, inclusive, are rotated and a new idle finder is allotted and, together with the associated secondary switch, is started in the usual manner. In the case now under discussion, the wipers of the allott'cr FA may pass over the contacts of busy tinder switches and secondary switches with the circuits for the stepping magnets of such switches prepared at armatures 77 and 74-.

' However, it is not possible to operate the 'ter cannot be stepped stepping magnets secondary switch, are disconnected at such ample, when connecting relay 25 of the find- I er F is operated, stepping magnet 2% is .disconnected at armature I0, and stepping magnet 35 is disconnected at armature 39.7

A further point that should beinentioned, perhaps, is that, although the finder FA can be stepped o'tia set o f'con'tacts while the finder F and the secondary switch SS are being operated, in case the secondary group becomes busy at such a time, the finder allototf a set of contacts secondary switch has because the auxiliary after the associated found an idle trunk test wiper 83 is disconnected at armature 63 I of test relay 66, which energizes when the Secondary switch finds an idle trunk, as here inbefore pointed out.

lVhat is claimed is: r

1. In a telephone system, lines, means including a plurality of backward hunting finder switches and a like number of forward hunting non-numerical switches for extending said lines when calling, said switches being connected together in pairs, eachpair consisting of, one backward hunt ing switch and one forward hunting switch, each of said switch-es having a stepping magnet and an operating circuit therefor, an allotter, means responsive to a call on one'of said lines for operating said allotter to directly close the circuit of the stepping magnet of an idle find-er to start it hunting for. the calling line and to directly close the circnit of the steppin'gmagnet of the associated forward hunting switch to start said forward hunting switch also.

2. In a telephone system, two secondary switches having access, respectively, to two different groups of trunks, means for starting one of said switches in search of an idle trunk, and means responsive to a busy condition appearing on all trunks in the associated group before a trunk is found by the last named switch for stopping such switch and for starting the other switch.

In a telephone system, a group of lines, a plurality of groups of trunks, a group of backward hunting switches for extending said lines, a plurality of groups of forward hunting switches, one group for each group of trunks and having access thereto, and cir-' cuit arrangements for connecting each of said backward hunting ward hunting switch in a separate group.

i. In a telephone system, a plurality of lines, a plurality of trunks divided into groups, a groupv of backward hunting switches having accessto said lines, a plurality of groups of forward hunting switches, one group for each of said groups of trunks and having access thereto, circuit connections between each of said backward hunting allotter switches with a for switches and a forward hunting switch in a separate one of said groups, said circuit connections including an intermediate distributing frame interposed between said backwardhunting switches and said forward hunting switches to facilitate grouping and re-grouping.

5. In a telephone system, a plurality of lines and a plurality of trunks, a pluralit of link circuits for connecting lines on whic 1 calls exist with idle trunks, each of said link circuits comprising a backward hunting tinderswitch for connecting with one of said lines and a forward hunting switch for selecting an idle trunk, a link allot-tel common to said links, two test relays in said allotter, means for energizing one of said test relays when the allotted backward hunting switch' has completed its operation, means for energizing the other of said relays when the allotted forward hunting switch has completed its operation, and means controlled by the said other testing relay for making the seized trunk busy regardless of whether the said backward hunting switch has completed its operation or not.

6. In a telephone system, a plurality of lines and a plurality of trunks, a plurality of link circuits forfconnecting said lines with said trunks each of said link circuits comprising a backward hunting finder switch for connecting'with one of said lines, a forward hunting switch for selecting an idle trunk, and a connecting relay for joining the two together, a link allotter common to said links, two test relays in said allotter, means for energizing one of said test relays when the allotted backward hunting switch has completed its operation, means for energizing the other of said relays when the allotted forward hunting switch has completed its operation, and means responsive to vthe completion of both energizations for energizing said connecting relay. I

7. In a telephone system, a plurality of lines and a plurality of trunks, a plurality of link circuits for connecting said lines with said trunks, each of said link circuits comprising a backward hunting finder switch for connecting with one of forward huntingswitcli for selecting an idle trunk, a link'allotter common to said links, two test relays in said allotter, means for energizing oneof said test relays when the allotted backward hunting switch has completed its operation, means for energizing the other of said relays'when the allotted forward hunting switch has completed its operation, and means responsive to the completion of both energ-izations for starting said allotter in search of another idle link circuit."

8. In a telephone system, a plurality of lines and a plurality of trunks, a plurality of link circuits for connecting said lines said lines and a 1 with said trunks, each of said link circuits comprising a backward hunting finder switch for connecting with one ot said lines and a forward hunting switch for selecting an idle trunk, each of said forward hunting switches having access to a separate group of trunks, testing means for advancing said allotter over busy link circuits, and auxiliary testing means for advancing said allotter over idle link circuits in case the associated trunks are all busy.

9. In a telephone system, a plurality of lines and a plurality of trunks, a plurality of link circuits l orconnecting said lines with said trunks, each of said link circuits comprising a backward hunting tinder switch for connecting with one oit said lines and a forward hunting switch "for selecting an idle trunk, each of, said. forward hunting switches having access to a separate group of trunks, testing means .tor advancing said allotter over busy link circuits, auxiliary testing means for advancing said allotter over idle link circuits in case the associated trunks are all busy, and means responsive to the completion oft the operation of the allotted forward hunting switch for rendering said auxiliary testing means inellect-ive.

10. plurality o t groups of lines, a plurality of groups of trunks, a group of finders assigned to each group ot lines, a group of secondary switches having access to each group of trunks, a distributing frame, and jumpers on said frame connecting said tinders and secondary switches together in pairs, said jumpers being so arranged that finders in each'group are paired with secondary switches in ditt'eren't groups.

V 11 In a telephone system, lines, means including a plurality ol backward hunting finder switches and a like number ol forward hunting non-mimeri'cal switches for extending said lines when calling, said switches being connected together in pairs, each pair comprising one backward l-i-un't-ing switch and one forward hunting switch, each of said switches having a stepping magnet and an operating circuit therefor, an allotter, means 7 responsive to a call on one of said lines for operating said allotte-r to directly close the circuit oi the stepping magnet of an idle finder to start it hunting for "the calling line and to directly close the circuit of the step ping magnet ot the associated forward hunting switch to start said forward hunting switch also, and means individual to each of said pairs of switches for disconnecting the associated stepping 'n'nignets to prevent them from being operated by said allotter when the switches are busy.

In a telephone system, two hunting switches, a plurality of lines terminating in bank contacts of one lninti'ng switch, a plurality of trim-ks terminating in bank contacts of the second hunting :wi'tcln'means for connecting said first and second hunting switches as a unit, an allotter for preselecting an idle unit, means responsive to the initiation of a call for rendering said allotter effective to cause said unit to hunt for the calling line and an idle trunk simultaneously and when both are found to connect the two.

13. In a telephone system, a calling line having a line relay and a cut-oil relay, said line relay operative responsive 'to a call, a line finder switch, having a connecting relay, and a trunk hunting switch connected to gether as a unit, an allotter switch for preselecting said unit and having a separate test relay for said finder and hunting switches, means responsive to'the operation of said line relay for rendering effective said allotter switch to cause said finder and hunting switches totind the calling line and an idle trunk, means responsive to the connection with said line for operating said finder switch test relay in series with said cut-oft relay, said cut-off relay remaining unoperated at this time, means responsive tot-he connection with said trunk tor operating said hunting switch test relay, means responsive to the operation of said test relays for operating said connecting relay, and means responsive to the operation of said connecting relay for operating said cut-ofi relay to disconnect said line relay from the calling line. M

in a telephone system, a group of lines, a group of double ended hunting switches each having access to all off the lines, a plurality of groups of trunks, each group of trunks being accessible to :a dili'e'ren't one oi? the switches, an allot-tor, means for operat ing the allotter responsive to the initiation ol. a call to cause a preselected switch to hunt for the calling line and to hunt for an idle trunk in its associated group of trunks, means i'n'the allotter operated when both the calling line and an idle trunk are found to disconnect the allotter from the switch and to select an idle switch tor sulisequent use,

Y means in each switch effective when :all

and the trunks accessible thereto are busy to cause the allotter to release the switch if it has been selected and to select a different switch. I

15. In 'a telephone system, a group of switches, a line accessible to all o l: said switches at one end thereof and different groups of trunks accessible to each of said switches in the other end thereof, an allotter associated with the line and with the group of switches, means in the allotter for pre selecting an idle switch having access toan idle trunk, means responsive to the initiation of a call for operating the preselected switch to hunt for the calling line and to hunt tor an idle trunk, means in the all-otter ft'or preselecnn a different switch when the previously selected switch finds the calling line and an idle trunk, and means for operating the allotter to select a different switch if before thepreviously selected switch finds a trunk all of the trunks accessible thereto become busy.

16. In a telephone system, a plurality of groups of trunks, a plurality of automatically operated switches eachhaving access to a diii'erent one of said device for preselecting an idle one of said switches, means for operating said preselected switch to select an idle trunk, a relay in said device arranged to be operated when a trunk isselected, means in said device operated under predetern'iined conditions whensaidrelay is operated, and operated if all trunks accessible tothe switch become busy before the relay operates, said means being effective when operating and selecting a different switch.

17. In a telephone system, a plurality of groups of trunks, a plurality of automatically operated switches each lr ving access to a group of trunks, a group of lines accessible to all of said switches, a device for presclecting an idle oneof said switches, means operated responsive to the initiation of a call on any of said lines for operating said preselected switch to hunt for the calling line and for an idle trunk, a relay in said device operated when an idle trunk is found. means for operating said device to select a different switch if all of the trunks accessi-. ble to the preselected switch become busy before said relay operates, and means forvopcrating said device to select a dili'erent switch when said relay operates and the calling line has been found.

18. In a telephone system, a plurality of lines, a plurality of groups of trunks, a switch associated wit-h each group of trunks, means operated responsive to the initiation of a call to cause one of said switches to hunt for the line over which the call was initiated and simultaneously therewith to hunt for groups of trunks, a

an idle'trunk of said group of trunks, means associated with each group of trunks and operated when all of the trunks in the. group are busy to stop the hunting movement of the switch associated with that group of trunks.

1%). In a telephone system, a line, a plurality of groups of trunks, a plurality of switches having access to each group 0t trunks, all of said switches having access to the line, an allotter for preselecting an idle switch, means responsive to the initiation of a call over the line to cause the preselected switch to hunt for the line and simultaneously therewith to hunt for an idle trunk, and means in the allotter for starting another switch having access to a difl'erent group of trunks hunting if all of the trunks accessible to said first selected switch become busy before said first selected switch finds an idle trunk. V

2(). 1n combination with a line and a plurality of trunks of a plurality of switches each for establishing connections between said-line and one of said trunks, an allotterfor selecting a switch, means for operatingsaid selected switch to hunt for an idle trunk and for the line, a relay in the allotter operated when an idle trunk is found, another relay in the allotter operated when both the line and a trunk are found, a motor magnet for operating the allotter, said motor magnet having contacts for interrupting its cir cult, means comprising front contacts on said first relay forshuntin said contacts, and means for establishing a stepping circuit for said magnet when all of the trunks accessible to the selected switch are busy, said means including baclt contacts on both of said relays.

' In witness whereof, I hereunto subscribe my name this 24th day of March, A. 1)., 1924 FRED T. MADSEN. 

